LX470 AHC issues - pressure sensor 1998 Vs. 2002 (2 Viewers)

[suprarx7nut]

I have no idea where this blue and red updates are, it would be best if you just add a complete new post.
Your case sounds oddly similar to my ongoing AHC epic. I had a failed pump, used removed AHC parts, including pump an old cruiser with unknown mileage. That later failed again - dying seagull noises, flashing off, car does not lift. That's when I found out that I can make it run again by driving it in reverse for 5-10 seconds.
Replaced the pump with a brand new pump, including fluid flush (old was dark, but clean), drove fine with it for 10k kilometres, then failed in the exact fricking same way.
Somewhere around this point I tried the same thing - plugged the pump hole with a finger and could stop the flow. Ran the motor in reverse and it was blasting again. I even played around with using the metal pipe that goes down to the attenuator that's bolted to the chassis, to use it as kind of a hose to pump fluid into a bottle and watch the flow when it was squealing.

I also have a broken accumulator bleeder and I keep flushing air out of the sphere bleeders. I am 99% sure that either my accumulator is full of air or as @IndroCruise mentioned - pump is sucking air from around the reservoir/pump/motor, but I doubt that. I have a spare accumulator, but I dread the thought of removing the old one with the ridiculous bolts on top of the chassis.
This came out after maybe 20k km of driving since I put the new pump and fluid. It ain't coke.

View attachment 3638040

Flushed with new fluid, everything settled, could go L <> H for the first time in ages. Could even do it multiple times in a row. I was sure I beat it and finally had working AHC. Drove like that for maybe 200-300km, including 50-100km hard offroad and the seaguls were back Got this out.

View attachment 3638041

Drove like that another 100-150km, all seemed good. Tried L<>H a few times, but unlike last time I had to run the pump in reverse a couple of times, otherwise seagulls. It was still working, but decided to check what is going on with the fluid - bubbles are building up already...

View attachment 3638051

Air is mostly coming from the rear right globe and some from the front right. Left side is mostly good. I am starting to suspect that globe(s) might be leaking.
Unfortunately can't really rely on the graduation test for that, as I am running non-AHC springs in the rear, due to a lot of added weight (RTT, awning, drawer system, aux water and fuel tanks, etc) and rear pressures are out of spec.


I should have removed the damned thing ages ago and installed conventional suspension, but I damn love the AHC ride when it was working and it was working for 280k miles on this car. Nothing else I have tried on friends cruisers comes even close to it and the comfort of adjusting between boaty Comfort and Sport from the cabin...

Don't know if there is something helpful for you in this post, but you are not alone

I'm guessing you just have a bad globe. Replace the corner with the most aeration. Bleed. If still aerating, there's another source. Bad globes happen. A few other folks have run into relatively new globes failing. Seems to have been some questionable quality polymer used in covid-era manufacture windows.

The gradation test is still pretty helpful even if you're way out of pressure spec. We've tested a bunch of 100 series with pressure WAY over and the impact is minimal. The difference before and after pressure-correction may only be a couple grads.

The gradation test is limited, though. You can have one totally dead globe leaking gas into the system, but if the other 3 globes are brand new, the overall fluid movement will look good.

Thankfully, globe swaps are quick and easy.

Also keep in mind the height accumulator is basically one big globe. That can fail too, and let out gas into the system. So same applies there. If you notice a ton of gas bubbles when bleeding at the accumulator, that can be a clue that the membrane in the accumulator is failing.


This is an evolving thought for me, but the order of likelihood failures as a total generalization for AHC in the 100 seem to be:

1. Bad globe releasing gas
2. Gel in the pump restricting inlet
3. Severed/shorted wires along left side frame rail near rear tire (testable at the large B1 connector in rear corner of frame)

@Moridinbg I know you've done a real extensive overhaul of the entire vehicle, so I expect most things are in very good shape. I'd swap a globe or two as you chase bubbles. High chance of success, I think. If that doesn't do the trick, seems like it must have debris in the inlet strainer. Typically though, I think the squeal comes from gas entrainment, not a blocked strainer. Of course, that could be wrong.

 

[suprasvobodea]

I'm guessing you just have a bad globe. Replace the corner with the most aeration. Bleed. If still aerating, there's another source. Bad globes happen. A few other folks have run into relatively new globes failing. Seems to have been some questionable quality polymer used in covid-era manufacture windows.

The gradation test is still pretty helpful even if you're way out of pressure spec. We've tested a bunch of 100 series with pressure WAY over and the impact is minimal. The difference before and after pressure-correction may only be a couple grads.

The gradation test is limited, though. You can have one totally dead globe leaking gas into the system, but if the other 3 globes are brand new, the overall fluid movement will look good.

Thankfully, globe swaps are quick and easy.

Also keep in mind the height accumulator is basically one big globe. That can fail too, and let out gas into the system. So same applies there. If you notice a ton of gas bubbles when bleeding at the accumulator, that can be a clue that the membrane in the accumulator is failing.


This is an evolving thought for me, but the order of likelihood failures as a total generalization for AHC in the 100 seem to be:

1. Bad globe releasing gas
2. Gel in the pump restricting inlet
3. Severed/shorted wires along left side frame rail near rear tire (testable at the large B1 connector in rear corner of frame)

@Moridinbg I know you've done a real extensive overhaul of the entire vehicle, so I expect most things are in very good shape. I'd swap a globe or two as you chase bubbles. High chance of success, I think. If that doesn't do the trick, seems like it must have debris in the inlet strainer. Typically though, I think the squeal comes from gas entrainment, not a blocked strainer. Of course, that could be wrong.

SupraRx7Nut
I have 4 brand new, OEM globes and a New Accumulator on my system(due to heard bleeder valve) , so I don't think there are any leaking N2 from the Globes or the Accum. The little fluid I was able to bleed by app;y 12V to the Pump AND 12V to the Accum solenoid to open it ( engine off due to 1762 repeatedly firing...) the fluid had Large bubbles - due to open lines and open shocks) which I expected. I do NOT have the tiny, soda pop-like fine bubbles that would come from high press N2 saturating the oil) .Im about to remove the reservoir and inspect the new pump assy for any issues there . When I applied 12BV directly to the pump and removed the outlet line, there was just a gentle stream of fluid, that I could stop with my gloved thumb or finger! This was surprising as I cannot do that with a garden hose at 25 psi !!! This pump is a high-pressure, direct displacement gear pump, there should be NO WAY that I can block the output with my finger. I will take a video of this tonight and post it on my continuous thread

 

[suprarx7nut]

SupraRx7Nut
I have 4 brand new, OEM globes and a New Accumulator on my system(due to heard bleeder valve) , so I don't think there are any leaking N2 from the Globes or the Accum. The little fluid I was able to bleed by app;y 12V to the Pump AND 12V to the Accum solenoid to open it ( engine off due to 1762 repeatedly firing...) the fluid had Large bubbles - due to open lines and open shocks) which I expected. I do NOT have the tiny, soda pop-like fine bubbles that would come from high press N2 saturating the oil) .Im about to remove the reservoir and inspect the new pump assy for any issues there . When I applied 12BV directly to the pump and removed the outlet line, there was just a gentle stream of fluid, that I could stop with my gloved thumb or finger! This was surprising as I cannot do that with a garden hose at 25 psi !!! This pump is a high-pressure, direct displacement gear pump, there should be NO WAY that I can block the output with my finger. I will take a video of this tonight and post it on my continuous thread

My response there in that last post was all to @Moridinbg .

I understand your situation is different.

Excited to see how you progress.

 

[IndroCruise]

SupraRx7Nut
I have 4 brand new, OEM globes and a New Accumulator on my system(due to heard bleeder valve) , so I don't think there are any leaking N2 from the Globes or the Accum. The little fluid I was able to bleed by app;y 12V to the Pump AND 12V to the Accum solenoid to open it ( engine off due to 1762 repeatedly firing...) the fluid had Large bubbles - due to open lines and open shocks) which I expected. I do NOT have the tiny, soda pop-like fine bubbles that would come from high press N2 saturating the oil) .Im about to remove the reservoir and inspect the new pump assy for any issues there . When I applied 12BV directly to the pump and removed the outlet line, there was just a gentle stream of fluid, that I could stop with my gloved thumb or finger! This was surprising as I cannot do that with a garden hose at 25 psi !!! This pump is a high-pressure, direct displacement gear pump, there should be NO WAY that I can block the output with my finger. I will take a video of this tonight and post it on my continuous thread

The following two posts are dense and picture heavy in response to requests:

On gases in AHC Fluid:

Suggest let's not get too distracted by "size of bubbles" unless you really want to get into the physical chemistry of solubility of various gases in a light mineral oil such as AHC Fluid -- if so, the internet is your friend. The point is that (a) physical entrainment of gas in oil and (b) chemical solubility of gas in oil are two different effects -- and both occur in the AHC system. Solubility of air (which is roughly 78% nitrogen, 21% oxygen, 1% other) and 'pure' (approximately 100%) nitrogen both increase with pressure and temperature (as does C02 which is irrelevant but provides a comparison).

As an analogy, consider a bottle of sparkling wine or soda pop drink -- very difficult to see any bubbles in the fluid in the bottle until the cork/cap/stopper is removed and the drink is poured. At this time, the incompressible fluid containing compressed gas is exposed to lower atmospheric pressure, then (a) entrained gas is released, and (b) dissolved gas desorbs -- and bubbles appear as gas reforms as it emerges from the fluid.

Bubble size, vigour and energy will have more to do with the pressure difference between the gas in the contained fluid until released and the atmospheric pressure, more than anything else. We could get into a discussion involving phase diagrams and reaction kinetics -- but that would be an unhelpful diversion.

Refer to the diagram of the hydraulic circuit posted previously at Post #69 in this thread. The pressure in the Front AHC system and Rear AHC system (they are separate, not hydraulically linked) will be at least the Front and Rear AHC pressures respectively, in that part of the hydraulic circuit behind the closed Levelling Valves (on the 'globe'/'shock absorber' side of the Levelling Valves) -- unless there is leakage somewhere. Gas solubility is different (lower -- so gas emerges) at atmospeheric pressure (which is about 0.1 Mpa) compared with higher solubility at (say) +/- 6 Mpa or more in either Front or Rear of the AHC system.

After a major repair -- such as replacement of 'globes', or 'shock absorbers', or 'AHC Pump sub-assembly Part Number 48901-60010', or 'pipelines', or other components or disturbances -- there will be plenty of free air initially at atmospheric pressure at multiple places in the system. This will be compressed and entrained or dissolved in the fluid when the AHC system is re-pressured by the Pump.

So the reminder by @suprarx7nut is very relevant. It avoids another assumption about 'globe' health. If, when bleeding, you see different effects at different 'globes', then suspect that the most bubbly 'globe' is leaking nitrogen from behind a faulty membrane. It is possible (if part of a manufacturing batch all with the same fault where the membrane is crimped and sealed to the 'globe' housing or where the protective 'button' is attached to the membrane) -- but it seems highly unlikely that all four new 'globes' will fail at the same time and give the same effect so soon after delivery and installation -- assuming they are all new geniune Toyota/Lexus OEM items, still in date and not too old -- and not cheap 'knock-offs' or second-hand 'globes'.

The Height Control Accumulator is a different kind of 'accumulator'. Instead of a membrane as in the 'globes', there is a piston and seals around the piston -- as seen in the previously posted diagrams in this thread. If your new Height Control Accumulator is bled until nothing comes out of the bleeder valve, then the Height Control Accumulator is empty of fluid UNLESS its nitrogen pressure has somehow been lost and/or the piston somehow has become stuck. However, when the Pump attempts to re-charge the Height Control Accumulator at the end of a LO > N or N > HI raise, it will do so with fluid from the AHC Tank. If the fluid in the AHC Tank is polluted with air or debris, then unless that fluid is arrested by the Inlet Strainer within the AHC Pump, that polluted fluid will arrive at the Height Control Accumulator and then be distributed all around the whole AHC system at the next raise, LO > N or N > HI.

Note that fluid returning from the AHC system passes directly to the AHC Tank -- it is directed by the Return Valve and passes around but not through the AHC Pump sub-assembly.

On 'sludge' and 'gel':

Let's make a clear distinction here.

There are numerous Posts on this and other forums concerning 'gel' polluting AHC/TEMS systems on 100 series vehicle and polluting the more advanced AHC/AVS system on 200 series vehicles -- on Lexus vehicles and Land Cruiser vehicles if AHC-equipped. This appears to relate to supply in the USA of AHC Fluid manufactured by Japanese oil company Idemitsu Kosan Co. Ltd, probably in their USA plant, and distributed in one-litre plastic bottles through Lexus and Toyota. We don't seem to have had this problem in the Rest of the World where fluid arrives in 2.5 litre steel cans and not in one-litre plastic bottles. There have been guesses but no chemically satisfactory explanation as to how or why the 'gel' is a problem in the one-litre plastic bottles.

Whatever, the 'gel' certainly obstructs flow through the Inlet Strainer, impedes Pump discharge, causes C1762 and some times C1751 as well, and possibly other DTC's. Please always check the FSM description of the relevant DTC's to understand what is happening, not just the cryptic summary on Techstream (which assumes FSM knowledge).

The AHC Pump then requires dismantling and cleaning -- by removing the Strainers -- Pump reversal does not cut it -- reversal may give some relief but the 'gel' is not far away, so the effect is short term and illusory. When the Pump is run in reverse, the fluid does not run in the reverse direction. The Pump cannot suck fluid past the closed Levelling Valves. Instead, fluid may (?) pass through the middle of meshing gears (rather than around the gear perimeter as is normal?? Need to check this) but still discharges at the normal discharge point on the Pump -- at much, much, much reduced efficiency. This needs to be tested this experimentally.

Cleaning out the AHC Tank is a good start. This has been done but if it needs a re-visit to eliminate all possibilities and assumptions about remnant 'gel' or 'sludge', please completely separate and remove the AHC Tank from the rest of the assembly. This also allows inspection of the seal below the Tank and the rest of the assembly. A poor seal here is an excellent opportunity for air to be drawn into the AHC system almost directly above the AHC Pump sub-assembly -- suggest don't hesitate, replace this seal -- Part Number 47255-60100 for USD4.74 at Partsouq. Suggest also consider replacing the AHC Tank -- Part Number 48930-60010 for USD83.83 at Partsouq when available -- suggest check IMPEX and local dealer prices.

'Sludge' has a different story but has the same effect as 'gel'. See hydraulic circuit diagram posted previously. On the low pressure side (Pump side) of the Levelling Valves, the pressure will be at atmospheric pressure all the way back to and including the AHC Tank -- including surrounding the AHC Pump sub-assembly UNLESS the AHC system is lowering the vehicle (Levelling Valves open, fluid is released back to the Tank), OR, the AHC system is raising the vehicle (Levelling Valves open, Pump starts, forces fluid to the 'shock absorbers' as struts), OR, the auto self-levelling feature of AHC is operating and moving fluid in either direction to achieve the correct height (as controlled by the height selector switch on the centre console, the Height Control Sensors and the ECU).

This means that AHC Fluid stagnates in various places for a lot of the time. One obvious low-flow/low-pressure region for stagnation is the region around the AHC Pump sub-assembly behind the outer cover as shown in the pic below (provided by @BullElk). It is no surprise that sludge forms here -- due to ageing of AHC Fluid and its additives, oxidation, temperature changes, low fluid flow, debris picked up within the system, moisture picked up because the AHC Tank is exposed to air, etc, etc, etc -- especially if good 'hydraulic hygiene' is not followed -- meaning routine AHC Fluid changes are not done per the frequency in the Owner's Manual (or preferably twice as often for better reliability and longevity).

Another stagnation region, although for different reasons, is the unswept volume (not swept by the piston) in the 'shock absorbers'. A further stagnation region is the long pipes connecting the system components -- fluid shuffles backwards and forwards in these pipes, end-to-end flow and fluid exchange happens only very slowly during vehicle operation.

The point is that this 'sludge' has been in the process of building up over time in a neglected AHC system ANYWAY. This 'sludge' is NOT caused by batches of bad fluid. It is an inevitable effect of old fluid steadily degrading and left in the system for too long.

However, the consequences are the same. When some of the 'sludge' breaks away, it inevitably arrives at the Inlet Strainer and causes a partial or complete blockage at the Inlet Strainer (and possibly the By-pass Strainer), preventing the AHC Pump from receiving fluid from the AHC Tank -- until eventually C1762 turns up, possibly with C1751 and possibly other DTC's -- and then "Active Test" cannot work until this fault is fixed.

The remediation is the same for 'sludge' and 'gel' -- the AHC Pump sub-assembly requires dismantling and cleaning -- by removing the Strainers, OR, it is necessary to replace the Pump.

Please note that even when the AHC Pump problem is resolved, you are NOT at the end.

You are at the beginning. You have written "I truly hope this will solve my 1762 fail-safe issue". I truly, truly hope that you may be so lucky .... but all that has happened so far is that I have pushed you to set aside assumptions and check the AHC Pump, even though it is new, with a very basic pressure and flow test and to deal with the findings, for which alternatives (1) to (8) were provided at Post #74 this thread -- with the suggestion that alternative (8) -- strainer blockage -- seemed most likely. The pictures in this Post and the next Post relate to these eight (8) alternatives.

There IS air in the AHC system on this vehicle -- you have seen it and reported it -- and C1762 may continue until persistent and repetitive bleeding removes the air. The method of doing this has been described in previous posts in this thread. More patience and perseverance may be required.

After looking at this post and the next one, please review again the pictures and comments in my previous Posts #51, #56, #69, #74 in this thread.

Hope all goes well!!

Internal layout of AHC Pump sub-assembly:

'Sludge' accumulating around AHC Pump sub-assembly (behind external cover with large "+" impressed on it):

"Notch" position on gear case relative to By-pass Strainer:

Withdrawing Inlet Strainer for inspection and cleaning (same method for By-pass Strainer):

 

[IndroCruise]

On gases in AHC Fluid:

Suggest let's not get too distracted by "size of bubbles" unless you really want to get into the physical chemistry of solubility of various gases in a light mineral oil such as AHC Fluid -- if so, the internet is your friend. The point is that (a) physical entrainment of gas in oil and (b) chemical solubility of gas in oil are two different effects -- and both occur in the AHC system. Solubility of air (which is roughly 78% nitrogen, 21% oxygen, 1% other) and 'pure' (approximately 100%) nitrogen both increase with pressure and temperature (as does C02 which is irrelevant but provides a comparison).

As an analogy, consider a bottle of sparkling wine or soda pop drink -- very difficult to see any bubbles in the fluid in the bottle until the cork/cap/stopper is removed and the drink is poured. At this time, the incompressible fluid containing compressed gas is exposed to lower atmospheric pressure, then (a) entrained gas is released, and (b) dissolved gas desorbs -- and bubbles appear as gas reforms as it emerges from the fluid. Bubble size and energy will have more to do with the pressure difference between the gas in the contained fluid until released and the atmospheric pressure than anything else.

The pressure in the Front AHC system and Rear AHC system (they are separate, not hydraulically linked) will be at least the Front and Rear AHC pressures respectively, in that part of the hydraulic circuit behind the closed Levelling Valves (on the 'globe'/'shock absorber' side of the Levelling Valves) -- unless there is leakage somewhere. Gas solubility is different (lower -- so gas emerges) at atmospeheric pressure (which is about 0.1 Mpa) compared with (say) +/- 6 Mpa or more in either Front or Rear of the AHC system.

After a major repair -- such as replacement of 'globes', or 'shock absorbers', or 'AHC Pump sub-assembly Part Number 48901-60010', or 'pipelines', or other components or disturbances -- there will be plenty of free air initially at atmospheric pressure at multiple places in the system. This will be compressed and entrained or dissolved in the fluid when the AHC system is re-pressured by the Pump.

So the reminder by @suprarx7nut is very relevant. It avoids another assumption about 'globe' health. If, when bleeding, you see different effects at different 'globes', then suspect that the most bubbly 'globe' is leaking nitrogen from behind a faulty membrane. It is possible (if part of a manufacturing batch all with the same fault where the membrane is crimped and sealed to the 'globe' housing or where the protective 'button' is attached to the membrane) -- but it seems highly unlikely that all four new 'globes' will fail at the same time and give the same effect so soon after delivery and installation -- assuming they are all the new geniune Toyota/Lexus OEM items, still in date and not too old -- and not cheap 'knock-offs' or second-hand 'globes'.

The Height Control Accumulator is a different kind of 'accumulator'. Instead of a membrane as in the 'globes', there is a piston and seals around the piston -- as seen in the previously posted diagrams in this thread. If your new Height Control Accumulator is bled until nothing comes out of the bleeder valve, then the Height Control Accumulator is empty of fluid UNLESS its nitrogen pressure has somehow been lost and/or the piston somehow has become stuck. However, when the Pump attempts to re-charge the Height Control Accumulator at the end of a LO > N or N > HI raise, it will do so with fluid from the AHC Tank. If the fluid in the AHC Tank is polluted with air or debris, then unless that fluid is arrested by the Inlet Strainer within the AHC Pump, that polluted fluid will arrive at the Height Control Accumulator and then be distributed all around the whole AHC system at the next raise, LO > N or N > HI.

Note that fluid returning from the AHC system passes directly to the AHC Tank -- it is directed by the Return Valve and passes around but not through the AHC Pump sub-assembly.

On 'sludge' and 'gel':

Let's make a clear distinction here.

There are numerous Posts on this and other forums concerning 'gel' polluting AHC/TEMS systems on 100 series vehicle and and polluting the more advanced AHC/AVS system 200 series vehicles -- on Lexus vehicles and Land Cruiser vehicles if AHC-equipped. This appears to relate to supply in the USA of AHC Fluid manufactured by Japanese oil company Idemitsu Kosan Co. Ltd, probably in their USA plant, and distributed in one-litre plastic bottles through Lexus and Toyota. We don't seem to have had this problem in the Rest of the World where fluid arrives in 2.5 litre steel cans and not in one-litre plastic bottles. There have been guesses but no chemically satisfactory explanation as to how or why the 'gel' is a problem in the one-litre plastic bottles.

Whatever, the 'gel' certainly obstructs flow through the Inlet Strainer, impedes Pump discharge, causes C1762 and some times C1751 as well, and possibly other DTC's. Please always check the FSM description of the relevant DTC's to understand what is happening, not just the cryptic summary on Techstream (which assumes FSM knowledge).

The AHC Pump then requires dismantling and cleaning -- by removing the Strainers -- Pump reversal does not cut it -- reversal may give some relief but the 'gel' is not far away, so the effect is short term and illusory. When the Pump is run in reverse, the fluid does not run in the reverse direction. The Pump cannot suck fluid past the closed Levelling Valves. Instead, fluid passes through the middle of meshing gears (rather than around the gear perimeter as is normal) but still discharges at the normal discharge point on the Pump -- at much, much, much reduced efficiency. You can test this experimentally.

Cleaning out the AHC Tank is a good start. This has been done but if it needs a re-visit to eliminate all possibilities and assumptions about remnant 'gel' or 'sludge', please completely separate and remove the AHC Tank from the rest of the assembly. This also allows inspection of the seal below the Tank and the rest of the assembly. A poor seal here is an excellent opportunity for air to be drawn into the AHC system almost directly above the AHC Pump sub-assembly -- suggest don't hesitate, replace this seal -- Part Number 47255-60100 for USD4.74 at Partsouq. Suggest also consider replacing the AHC Tank -- Part Number 48930-60010 for USD83.83 at Partsouq when available -- suggest check IMPEX and local dealer prices.

'Sludge' has a different story but has the same effect as 'gel'. See hydraulic circuit diagram posted previously. On the low pressure side (Pump side) of the Levelling Valves, the pressure will be at atmospheric pressure all the way back to and including the AHC Tank -- including surrounding the AHC Pump sub-assembly UNLESS the AHC system is lowering the vehicle (Levelling Valves open, fluid is released back to the Tank), OR, the AHC system is raising the vehicle (Levelling Valves open, Pump starts, forces fluid to the 'shock absorbers' as struts), OR, the auto self-levelling feature of AHC is operating and moving fluid in either direction to achieve the correct height (as controlled by the height selector switch on the centre console, the Height Control Sensors and the ECU).

This means that AHC Fluid stagnates in various places for a lot of the time. One obvious low-flow/low-pressure region for stagnation is the region around the AHC Pump sub-assembly behind the outer cover as shown in the pic below (provided by @BullElk). It is no surprise that sludge forms here -- due to ageing of AHC Fluid and its additives, oxidation, temperature changes, low fluid flow, debris picked up within the system, moisture picked up because the AHC Tank is exposed to air, etc, etc, etc -- especially if good 'hydraulic hygiene' is not followed -- meaning routine AHC Fluid changes are not done per the frequency in the Owner's Manual (or preferably twice as often for better reliability and longevity).

Another stagnation region, although for different reasons, is the unswept volume (not swept by the piston) in the 'shock absorbers'. A further stagnation region is the long pipes connecting the system components -- fluid shuffles backwards and forwards in these pipes, end-to-end flow and fluid exchange happens only very slowly during vehicle operation.

The point is that this 'sludge' has been in the process of building up over time in a neglected AHC system ANYWAY. This 'sludge' is NOT caused by batches of bad fluid. It is an inevitable effect of old fluid steadily degrading and left in the system for too long.

However, the consequences are the same. When some of the 'sludge' breaks away, it inevitably arrives at the Inlet Strainer and causes a partial or complete blockage at the Inlet Strainer (and possibly the By-pass Strainer, preventing the AHC Pump from receiving fluid from the AHC Tank) -- until eventually C1762 turns up, possibly with C1751 and possibly other DTC's -- and then "Active Test" cannot work until this fault is fixed.

The remediation is the same for 'sludge' and 'gel' -- the AHC Pump sub-assembly requires dismantling and cleaning -- by removing the Strainers, OR, it is necessary to replace the Pump.

Internal layout of AHC Pump sub-assembly:

View attachment 3638372

View attachment 3638373

"Notch" position on gear case relative to By-pass Strainer:

View attachment 3638375

Withdrawing Inlet Strainer for inspection and cleaning (same method for By-pass Strainer):

View attachment 3638376

MORE PICTURES -- SEE PREVIOUS POST FIRST:
Withdrawing Inlet Strainer for inspection and cleaning (same method for By-pass Strainer) -- Pic 2:

Pump sub-assembly internals:

Detail of Pump Body, Gears, Gear Carriers:
Note the following at the picture below:

• See position of O-rings on the Gear Carriers,
• Check condition of O-rings, replace as necessary as recommended by @BullElk,
• Composite back-up rings which fit between the O-rings and the end-cap of the AHC Pump sub-assembly with the "triangular" O-ring,
• Check condition of the back-up rings,
• Check condition of the "triangular" O-ring,
• Check condition of gears -- look for uneven wear on teeth,
• Check condition of Pump body -- look for signs of wear, looseness of fit,
• When assembling the Pump, push composite back-up rings into the end-cap, not on top of the O-rings, AND, double-check the position of the "notch" in the one of the Gear Carriers, then reassemble taking care not to over-tighten (to torque the short bolts, use FSM guidance for the longer bolts which attach the Pump sub-assembly to the overall assembly),
• When reassembled, the gears should turn easily with the fingers -- if not, something is wrong, either the end-cap is too tight, OR, the O-rings and back-up rings are not correctly seated -- FIX,

The above details are really important -- especially the correct position, seating and condition of all o-rings, back-up rings and seals -- if not addressed correctly, the Pump will perform poorly or may not work at all. As gear pumps go, this is a micro-pump and all tolerances are very fine.
ENLARGE THIS NEXT PICTURE TO SEE O-RINGS AND BACK-UP RINGS ON THE GEAR CARRIERS:

If the Pump Body is degraded as shown below, replace the Pump sub-assembly. If considering a second-hand Pump but cannot dismantle and check, best to forget it and buy new from IMPEX or PARTSOUQ or MEGAZIP or AMAYAMA.

 

[2001LC]

Revelation after revelation

Bottom line. AHC had no issues. Parts replaced, issue bagan.
The last revelations i saw posted, that caught my eye:

1. "Replaced "O-rings".
2. "I did remove the 2 cap screws - just to look at the gears , but i DID NOT REMOVE THEM . i was just curious as to the tolerance of them compared to my old pump. I knew that there was a notch in it and i did NOT NEED TO TAKE ANY CHANCES messing it up!!!!.....
3. Seems somewhere I read: You jump the pump with 12V, while hardline off pump. Little to no flow or pressure. I also read you clean the reservoir, use a tin of 2.5L jell free Toyota AHC fluid. If it not been for new pump or no issues beforehand. I think, jell in passages. But that can't be since all new and all clean. Unless somehow we have the first reported case of a 2.5L tin with jell.

I'd look at the cap screws and O-rings. @IndroCruise has give all you need.

It's been suggested more than once, you post pictures. They are worth a thousand words. Personally, I take a ton of pictures. The pre and during disassembly pictures are so helpful, during assembly.

 

[suprasvobodea]

So I have captured a part below of your UPDATE 4 >>> 5/21/24 -ADDITIONAL INFO IN RED ABOVE to make it easier for others such as @2001LC , @suprarx7nut , @BullElk , @Moridinbg or anybodyelse familiar with the internal details of the AHC Pump (or any gear pump) to help with the diagnosis and offer comments on the symptoms described and also critique my interpretation below:

@suprasvobodea >> UPDATE 5/21>>>> " HOUSTON ... WE HAVE A PROBLEM!! " - When i removed the flare nut from outlet of pump assy , and had 12V applied running, i was able to STOP THE FLOW OF OIL WITH MY THUMB!! There is NO WAY to prevent even a garden house with 30 psi pressure to prevent water from exiting with your thumb!!!!! WHen i removed my thumb, there was a weak stream of oil . SO .... THERE MUST BE SOMETHING GOING ON WITH THE NEW PUMP I INSTALLED FROM IMPEX! The question is , WHAT DO I DO NOW? I know i need to remove the pump assy and but what do i look for with a new pump gear set from the factory? How can a brand new pump NOT WORK PROPERLY?? Is this the source of my problem? it sure is suspicious!!

@IndroCruise: If poor AHC Fluid pressure and flow delivery from the recently installed new OEM AHC Pump from IMPEX is as you describe, then the following possibilities come to mind:

1. There is a problem with the motor driving the AHC Pump -- this seems most unlikely and I think that you would sense any motor problems when you were running the Pump directly from a 12 volt battery, OR,
2. The seal at the small drive connector between the Electric Motor and the Pump is damaged or not seated properly and allowing the AHC Pump to suck air, OR,
3. The small drive connector between the Electric Motor and the Pump somehow has become un-seated and is not engaging properly with the Motor or the Pump, causing the Pump not be driven properly, OR,
4. When you took the cover off the new AHC Pump sub-assembly to inspect the gears, the composite back-up rings which sit on top of the o-rings on each of the two gear carriers, or these two o-rings themselves, may have become slightly dislodged. If so, this would cause these two o-rings not to seal properly and this would allow fluid to by-pass internally within the AHC Pump, passing through the by-pass strainer back to the Inlet side of the Pump -- meaning some fluid would be re-circulating, causing low delivery flow and pressure at the Pump discharge, OR,
5. The triangular-looking seal (like an o-ring) on the underside of the cap-plate of the AHC Pump sub-assembly is damaged or not seated properly -- a failure of this seal would have the same affect as item (3) above,
6. The two gears and the gear carriers are not seated properly -- this would have the same affect as item (3) and item (4) above, OR,
7. The set of two gear carriers have been wrongly installed with "notch" on the Discharge side of the Pump. This should be on the Inlet side below the by-pass strainer. If not correct, the Pump cannot deliver correct flow and pressure and may barely work at all, OR,
8. The Inlet Strainer (and possibly but less likely the By-pass Strainer) may be fully or partially blocked with debris from within the system, OR, by sludge which inevitably builds up within the sysyem and may have been disturbed as a result of component change-outs OR may arise from incorrect non-AHC Fluid used at some time in the history of the vehicle, OR, gel which seems to have arisen in defective AHC Fluid in the USA market (associated with the one-litre plastic bottles). Any of these causes would inhibit fluid being drawn from the AHC Tank into the AHC Pump.

All of the above are possible, especially in an AHC Pump which has been disturbed internally.

Of these alternatives, item (8) -- Inlet Strainer partial or complete blockage -- seems more likely than the other alternatives.

Any of the above alternatives would result in C1762 .

The above explanation also may help in understanding why "Active Test" will not operate -- C1762 is designed conservatively to protect the AHC Pump and the AHC system. "Active Test" is not designed as a method of by-passing this protection in the presence of faults and causing damage -- in a similar way that bridging out a failed fuse or open circuit breaker is not a smart thing to do in an electrical circuit -- the cause has to be identified.

The next step is to remove and disassemble the AHC Pump sub-assembly and look for which of above alternatives is the cause of the poor performance of the AHC Pump. This is not difficult and it is easily fixable. If the above notes are are not clear, I am happy to supply some pictures on request which may help, including removal and cleaning of the Strainers. By the way, please do not assume that the Strainers can be cleaned simply by reversing the direction of rotation of the AHC Pump. This does not, and cannot, reverse the direction of fluid flow through the Strainers or through the Pump.

OR, another AHC Pump sub-assembly could be installed if disinclined to dismantle and examine the internals of the existing AHC Pump sub-assembly.

Please note that even when the AHC Pump problem is resolved, there IS air in the AHC system on this vehicle -- you have seen it and reported it -- and C1762 may continue until persistent and repetitive bleeding removes the air. The method of doing this has been described in previous posts in this thread.

Hope this helps!!

UPDATE 5 5/30/24

I listened to you guys and have added pictures and even a few videos to help ya'll help me!

I'll start with the disassembly of the new pump assy to check the o-rings and screens. I have pictures of the new pump halves and the position of the notch and gear. I also ordered a new grommet Part Number 47255-60100 between the tank and metal pump. Also, ALL 3 O-rings ( the small one inside the pump, the motor end seal, and the large pump cover O ring are ALL new as well. When I removed the large cover, there was a very small amount of sludge as I have pointed out in a photo, but a few particles. I removed both screens (inlet and return ) inside the pump halves, which were spotless. I back-sprayed with Brake cleaner just to be sure! ( see pictures) . Overall,.... the new pump and screens are very clean. The video of the outlet with 12V shows a straight stream which is good. What I don't understand is why I can stop the oil outlet by simply blocking it with my gloved finger??!?! Maybe this is normal, .. I don't know. But I understand this is a positive displacement gear pump, which builds very high pressure. .... so what am I missing..?
PSS> WHen I tried to upload 2 videos, I got an error message that .MOV files are not allowed so I guess I won't be able to show the stream of Oil out of the pump, but it was pretty strong... it blasted the valve cover opposite with oil so It appears to be pumping well. but I can still stop the flow with my finger.!




I believe this is the INLET strainer ?

Here is the NOTCH position of the new pump. It is correct from factory.

...and this the return strainer? maybe I have them reversed, but they were BOTH CLEAN!

Below is the motor end of the pump :

I finally received the NEW PS and I have the new grommet to install between the reservoir & pump. After I fill it with Oil, and run it with direct 12V to purge air from the internals before connecting the outlet line., I'll give another update later today in a couple of hours .... ( HOPEFULLY>>>>>... this will finally solve the 1762 fail-safe code and then all I have to do is BLEED.... BLEED .... BLEEED until the rain here stops!

Since I opened up the system again, I will have to apply 12V directly to BOTH the accumulator solenoid and pump to fill the solenoid with oil so I can begin to bleed the system globes. That seems to be the ONLY way to get Oil to the accumulator since the failsafe (1762) triggers immediately every time I try an ACTIVE TEST. I'll have to post the videos after I post this reply, as I get messages that only 5 pictures are allowed.. Why are we limited to just 5 photos?



This is a photo of the pump cover with a few particles of sludge ... or something. This doesn't appear to be a major issue....

UPDATE >>>> 5/31

I installed the New PS and the new grommet ( between the tank and pump) and filled the tank 1/3 full. I purged the pump before I installed the tank by putting oil directly into the inlet and angeled the pump to burp the air from the gears and cover to ensure that there was NO AIR inside the pump assy. Then I applied 12V to the assembled (whole unit > tank /pump switches) and blocked the outlet with my finger. The oil was leaking from the outlet, HOWEVER, THERE WAS NO LONGER A STREAM OF OIL UNDER DIRECT VOLTAGE~!!! It WAS working before I opened it up, checked /cleaned screens, and took the pictures I posted. NOW, it no longer works! There is NO STREAM like there was in my video before removing it.

I took it apart again,, and checked all the orientations of the O-ring and pressure ring ( fine), the notch location - Fine; free spinning of the gears by hand after tightening the 2 Allen screws,(very loose when turned by hand). NOW, I am really confused.????!!! This is my conundrum:

1. I have a brand new pump assy that has never been used.
2. It was working before I removed it to check the strainers and notch location from the factory ( all good and clean)
3. BEFORE REMOVING from LX>> Even though it had a stream of oil when I removed my finger, I could prevent the flow of oil with a light covering or with a rubber stopper inserted in the threaded hole. This seems very odd to me. I can't purge my system or fill the Accumulator if I have no fluid pressure. I made sure to push composite back-up rings into the end-cap, not on top of the O-rings, AND, double-check the position of the "notch" in one of the Gear Carriers, then reassemble taking care not to over-tighten
4. There are NEW O-rings on the motor side, the small internal inlet o ring, and the large Oring for the cover over the pump, and a grommet between the tank and pump.

SO>>>>>>>>> What should I do next ..? short of ordering ANOTHER new pump assy?

 

[suprasvobodea]

Revelation after revelation

Bottom line. AHC had no issues. Parts replaced, issue bagan.
The last revelations i saw posted, that caught my eye:

1. "Replaced "O-rings".
2. "I did remove the 2 cap screws - just to look at the gears , but i DID NOT REMOVE THEM . i was just curious as to the tolerance of them compared to my old pump. I knew that there was a notch in it and i did NOT NEED TO TAKE ANY CHANCES messing it up!!!!.....
3. Seems somewhere I read: You jump the pump with 12V, while hardline off pump. Little to no flow or pressure. I also read you clean the reservoir, use a tin of 2.5L jell free Toyota AHC fluid. If it not been for new pump or no issues beforehand. I think, jell in passages. But that can't be since all new and all clean. Unless somehow we have the first reported case of a 2.5L tin with jell.

I'd look at the cap screws and O-rings. @IndroCruise has give all you need.

It's been suggested more than once, you post pictures. They are worth a thousand words. Personally, I take a ton of pictures. The pre and during disassembly pictures are so helpful, during assembly.

 

[Moridinbg]

If you put the pump together, but with the notch on the other side, I am willing to bet that it will work. I have been there.

 

[suprasvobodea]

If you put the pump together, but with the notch on the other side, I am willing to bet that it will work. I have been there.

The pictures I took were a new disassemble pump that just separated the halves . It shows the notch by the inlet opening- per Indrocruise instructions. The gears turn freely, there are 3 new O rings , … there is something else thst I’m missing….. I just don’t know what it is

 

[Moridinbg]

This is where I noticed that running the motor in reverse allows it to pump again - RTH needed - seemingly air in AHC, car in Low, stuck in Patagonia - https://forum.ih8mud.com/threads/rth-needed-seemingly-air-in-ahc-car-in-low-stuck-in-patagonia.1300130/post-14724351 I played with redirecting the tube coming down from the pump and pumping into a bottle, to observe the stream and pressure.

This is where I noticed that putting the pump gears backwards allows it to pump again, after it stopped following a disassembly - RTH needed - seemingly air in AHC, car in Low, stuck in Patagonia - https://forum.ih8mud.com/threads/rth-needed-seemingly-air-in-ahc-car-in-low-stuck-in-patagonia.1300130/post-14725988

Gears turn freely, good O-rings, cleaned meshes. It's a mystery.

This was in Patagonia after 20k km trip around Chile & Argentina. We did 32k km more through Bolivia, Brazil, Peru, Colombia with the AHC barely holding. Luckily, a wire broke in the solenoids harness and prevented the pump from activating much.

 

[suprasvobodea]

U{DATE 7 -6/5/24 _ The saga continues...

I disassembled the NEW pump again, to check the location of the notch. I have a picture below of its position. Per INDOCRUISE, the notch is toward the inlet which he said is the low-pressure side. ! When I applied 12V to the pump, the horrible thing was ..... IT DID NOT PUMP A STREAM FROM THE OUTLET. It DID, when I checked in on the LX and again when it was removed and just propped on the radiator !! But when i carefully reassembled it, AND the notch is per the picture below after I disassembled it , it FAILED TO PUMP!
Remember, this is a BRAND NEW pump, never been used! and now it does not pump! PLEASE, can someone, tell me what is wrong with a brand new pump that does NOT WORK? I inserted the backup seal for the gear into the other half of the mating part and the O-ring onto the gear shaft - per INDOCRUISE details above in post #85. My parts look like his in the same post.
ANOTHER NOTE; and this could be important to more experienced hands than mine................ When I applied 12V directly in the correct polarity, it spun and hummed nicely- NO aeration or noise. HOWEVER.... when I reversed the polarity, the pump did NOT MOVE. The leads got very hot in 5- 8 seconds, which tells me something is wrong. ! I can move the gears in both directions when i remove the motor to get access to the direct drive notch. The motor ran in BOTH directions when it was removed from the pump housing... so I know the motor is good. But why is my new pump, LOCKED, and not working in the reverse direction ..? INDOCRUISE, SUPRARX, 2001LC,.... anybody ever have this happen to them ..? Could this be why it is NOT pumping oil in normal polarity .?

Remember, I used a screwdriver in the notch when the motor was removed, and could freely turn in both directions. But connected .... it almost melted the leads because the pump was locked up. But runs great in the correct polarity .

I MUST leave to go up to Wisconsin in 8 days .. and need to get this car working It's been 4 months since I have been able to use it. WHAT the heck to I try or do next ? I don't think disassembling the pump 5,6,7, or... times will do anything. Do I need to buy another NEW pump assy now ?? or what.

These are the positions of the two gears and halves.

Now, I have a new pump, that does NOT work when 12V is applied, I can hear, and feel it spin, but Oil only drips out of the outlet.!!!! UGH!!!!!!!!!!!! I need this LX working and driveable in the next 8 days !
HELP ME OBIE WON KENOBIE... your my only hope ..!

 

[2001LC]

If you still have your old pump. Install it.
or
If you've a good relationship, with your parts man at Toyota. Have him warranty your new pump. (Note: Typically you can not return electrical parts once installed. But they do carry a 1 year warranty)
or
Check in your area, for take-off parts, from AHC delete.

I've never disabled, assembled or even replace an AHC pump or motor. These pump typically get very little use over the years and only on for seconds when they do run, so last for many many years.

The only time I've jump a pump with 12 volts, was during testing. I found my ~22 gauge wires and tiny alligator clips (attached into motors wire housing block), couldn't handle the load, getting hot fast. So I built a test wire harness with old 12 gauge extension cord and a motors' wire housing block. Now, I just plug in and clip on battery.

 

[suprarx7nut]

I don't have any new words of wisdom. I don't have the pump assembly memorized.

I would be surprised if your old pump was bad.

I would be even more surprised that the old one was bad AND a brand new one was also bad.

If you have a pump that at any point recently moved fluid in the system, I'd install that and do all you can to force it to run.

New idea that might be completely useless and dangerous... To overcome the pressure fault, can you supply the expected voltage using your own power source at the wiring plug? IE a couple AA's in a little battery holder?

Sorry your system is so uncooperative. That's certainly frustrating.

 

[suprasvobodea]

I don't have any new words of wisdom. I don't have the pump assembly memorized.

I would be surprised if your old pump was bad.

I would be even more surprised that the old one was bad AND a brand new one was also bad.

If you have a pump that at any point recently moved fluid in the system, I'd install that and do all you can to force it to run.

New idea that might be completely useless and dangerous... To overcome the pressure fault, can you supply the expected voltage using your own power source at the wiring plug? IE a couple AA's in a little battery holder?

Sorry your system is so uncooperative. That's certainly frustrating.

UPDATE >>> 6-8-25

At this stage, after 4 months of inoperative use of my LX... I am at the end of my rope, at the knot.... and getting depressed! I need to use this in 7 days to go home to Wisconsin, and I don't know what to do anymore. I ordered another brand new pump assy from IMPEX for $102 now. the last one was $92 so they had a price increase too !) I will NOT OPEN IT this time! and install it right from the box.
What gets me, is I cannot get a stream of oil now when I apply 12V directly to it?!?!?!?? It DID pump a stream out before I removed it from the LX and did a direct 12V........... so something happened ...l just don't know what.
AND .. WHY won't my pump work when I reverse the polarity (make it run backward...??????_ It made the leads VERY VERY hot in 5 seconds cause it was locked up! -- That is not right.

I hate to say this, but knowing now, this horrible nightmare, I would NEVER, EVER replace the shock bushings, or open up this system .... If I knew about the 1762 code nightmare ..... I would have left the accumulator broken bleen valve alone and just never bleed it. I KNOW there is air in the system - per INDOCRUISE and everyone else, but now I can not even get the frickin PUMP to work.?? And all I did was take it apart to check the little screen,, and they were clean! Moridingbg suggested I reverse the gear bearing sleeves, so the notch is on the other side. I don't know if that will make the pump work, and will change it back, but at this stage........ I don't know what to do

 

[suprasvobodea]

MORE PICTURES -- SEE PREVIOUS POST FIRST:
Withdrawing Inlet Strainer for inspection and cleaning (same method for By-pass Strainer) -- Pic 2:
View attachment 3638380

Pump sub-assembly internals:
View attachment 3638379

Detail of Pump Body, Gears, Gear Carriers:
Note the following at the picture below:

• See position of O-rings on the Gear Carriers,
• Check condition of O-rings, replace as necessary as recommended by @BullElk,
• Composite back-up rings which fit between the O-rings and the end-cap of the AHC Pump sub-assembly with the "triangular" O-ring,
• Check condition of the back-up rings,
• Check condition of the "triangular" O-ring,
• Check condition of gears -- look for uneven wear on teeth,
• Check condition of Pump body -- look for signs of wear, looseness of fit,
• When assembling the Pump, push composite back-up rings into the end-cap, not on top of the O-rings, AND, double-check the position of the "notch" in the one of the Gear Carriers, then reassemble taking care not to over-tighten (to torque the short bolts, use FSM guidance for the longer bolts which attach the Pump sub-assembly to the overall assembly),
• When reassembled, the gears should turn easily with the fingers -- if not, something is wrong, either the end-cap is too tight, OR, the O-rings and back-up rings are not correctly seated -- FIX,

The above details are really important -- especially the correct position, seating and condition of all o-rings, back-up rings and seals -- if not addressed correctly, the Pump will perform poorly or may not work at all. As gear pumps go, this is a micro-pump and all tolerances are very fine.
ENLARGE THIS NEXT PICTURE TO SEE O-RINGS AND BACK-UP RINGS ON THE GEAR CARRIERS:
View attachment 3638381

If the Pump Body is degraded as shown below, replace the Pump sub-assembly. If considering a second-hand Pump but cannot dismantle and check, best to forget it and buy new from IMPEX or PARTSOUQ or MEGAZIP or AMAYAMA.

View attachment 3638386

IndoCruise
I disassembled the NEW pump again, to check the location of the notch. I have a picture below of its position. The notch is toward the inlet which you said is the low-pressure side. ! When I applied 12V to the pump, the horrible thing was ..... IT DID NOT PUMP A STREAM FROM THE OUTLET. It DID, when I checked it on the LX and again when it was removed. But when I carefully reassembled it, AND the notch is per the picture below after I disassembled it , it FAILED TO PUMP- NO STREAM like it did when I checked it in situ.!
Remember, this is a BRAND NEW pump, never been used! and now it does not pump! PLEASE, can you, tell me what is wrong with a brand new pump that does NOT WORK? I inserted the backup seal for the gear into the other half of the mating part and the O-ring onto the gear shaft - per your instruction details above in post #85. My parts look like yours in that post.
ANOTHER NOTE; and this could be important to more experienced hands than mine................ When I applied 12V directly in the correct polarity, it spun and hummed nicely- NO aeration or noise. HOWEVER.... when I reversed the polarity, the pump did NOT MOVE. The leads got very hot in 4-6 seconds, which tells me something is wrong! I can move the gears in both directions when I remove the motor to get access to the direct drive notch. The motor ran in BOTH directions when it was removed from the pump housing... so I know the motor is good. But why is my new pump, LOCKED, and not working in the reverse direction ..? INDOCRUISE, SUPRARX, 2001LC,.... anybody ever had this happen to them ..? Could this be why it is NOT pumping oil in normal polarity .?

Remember, I used a screwdriver in the notch when the motor was removed, and could freely turn in both directions. But connected .... it almost melted the leads because the pump was locked up. But runs great in the correct polarity .

I MUST leave to go up to Wisconsin in 8 days .. and need to get this car working It's been 4 months since I have been able to use it. WHAT the heck to I try or do next ? I don't think disassembling the pump 5,6,7, or... times will do anything. Do I need to buy another NEW pump assy now ?? or what.

These are the positions of the two gears and halves.

Now, I have a new pump, that does NOT work when 12V is applied, I can hear, and feel it spin, but Oil only drips out of the outlet.!!!! UGH!!!!!!!!!!!! I need this LX working and driveable in the next 8 days !
HELP ME OBIE WON KENOBIE... your my only hope ..!

 

[suprarx7nut]

Your gear orientation appears correct according to my reference photos when I dismantled a pump.

My attempt at helping here:

1. Assume the pumps were always perfectly fine. They weren't broken before and they're not broken now.
2. Assume the reason you weren't/aren't seeing flow is a priming issue and/or air in the lines downstream.
3. Assume the fix is simply getting that pump full of fluid and purging gas from the system.

Those assumptions aside:

Install the new pump.
Get the reservoir full of fluid.
Connect via Techstream or your OBD2 app of choice that can see AHC data - do this to watch temp on the pump to avoid any crazy over-temp situations.
Unplug the pump connector from the car.
Make your own circuit with 10ga or larger wires and crimped on quick disconnect spade terminals and a switch of some sorts.
I have no idea how an AHC pump usually performs with no line attached to the outlet so I have no advice there.
Plumb the lines to the pump normally.
Remove the reservoir from the pump.
I assume there's a small column of fluid you can now see which leads into the pump.
Click the pump on with your makeshift switch.
Does fluid move? Quickly?
Tell us, preferably with pics.






Now, if it moves quickly, refill it. Move quickly still?

If so, check that reservoir for blockage. Any chance it's just not allowing fluid to flow in? Perhaps a blockage from debris disturbed during your overhaul. If you can't see anything in the reservoir causing issues, install it again. Now do the same little test. give it a little click on and listen to the pump. Same sound? same presumed fluid movement? If so, you're moving fluid and the goal is to get creative to purge gas from the system.

If the above method doesn't move fluid, I'm not sure what to do. The pump is a very simple mechanism. If it spins, it should pump. @BullElk messed around with an o-ring and had some resolution to his situation. @Moridinbg had a crazy experience in South America with multiple pumps that ran into the same code. Outside of those instances, we've seen countless other people fighting purging issues. Once purged, all is well.... normally.

 

[IndroCruise]

IndoCruise
I disassembled the NEW pump again, to check the location of the notch. I have a picture below of its position. The notch is toward the inlet which you said is the low-pressure side. ! When I applied 12V to the pump, the horrible thing was ..... IT DID NOT PUMP A STREAM FROM THE OUTLET. It DID, when I checked it on the LX and again when it was removed. But when I carefully reassembled it, AND the notch is per the picture below after I disassembled it , it FAILED TO PUMP- NO STREAM like it did when I checked it in situ.!
Remember, this is a BRAND NEW pump, never been used! and now it does not pump! PLEASE, can you, tell me what is wrong with a brand new pump that does NOT WORK? I inserted the backup seal for the gear into the other half of the mating part and the O-ring onto the gear shaft - per your instruction details above in post #85. My parts look like yours in that post.
ANOTHER NOTE; and this could be important to more experienced hands than mine................ When I applied 12V directly in the correct polarity, it spun and hummed nicely- NO aeration or noise. HOWEVER.... when I reversed the polarity, the pump did NOT MOVE. The leads got very hot in 4-6 seconds, which tells me something is wrong! I can move the gears in both directions when I remove the motor to get access to the direct drive notch. The motor ran in BOTH directions when it was removed from the pump housing... so I know the motor is good. But why is my new pump, LOCKED, and not working in the reverse direction ..? INDOCRUISE, SUPRARX, 2001LC,.... anybody ever had this happen to them ..? Could this be why it is NOT pumping oil in normal polarity .?

Remember, I used a screwdriver in the notch when the motor was removed, and could freely turn in both directions. But connected .... it almost melted the leads because the pump was locked up. But runs great in the correct polarity .

I MUST leave to go up to Wisconsin in 8 days .. and need to get this car working It's been 4 months since I have been able to use it. WHAT the heck to I try or do next ? I don't think disassembling the pump 5,6,7, or... times will do anything. Do I need to buy another NEW pump assy now ?? or what.

These are the positions of the two gears and halves.

Now, I have a new pump, that does NOT work when 12V is applied, I can hear, and feel it spin, but Oil only drips out of the outlet.!!!! UGH!!!!!!!!!!!! I need this LX working and driveable in the next 8 days !
HELP ME OBIE WON KENOBIE... your my only hope ..!

@suprasvobodea -- you certainly have had more than a fair share of frustrations!! Hopefully a fix soon emerges.

The above Posts from @suprarx7nut and @Moridinbg contain excellent leads based on their deep knowledge and experience -- it is always worth following these guys ….

To add a bit more, a ‘long check list’ has been created in this very long Post. It may be TLDR – apologies offered, past mid0night on the East Coast of Australia, too late to try to reduce the length.

The limitation of trying to provide assistance on a Forum such as this is that the vehicle cannot be seen nor heard nor felt by ‘advisors’ on IH8MUD and coordinating phone calls across international time zones is too difficult -- and so misunderstandings and wrong conclusions are all too easy!

The ideas below are meant to provide @suprasvobodea with information along with some comments -- a range of items to be considered -- a ‘check-list’. @suprasvobodea will know what has been done and what merits further attention in the list below and what is not worth further effort.

Actual Part Numbers checked at the Partsouq website have been used to identify component parts and avoid confusion where different people may use slightly different words (for example, between different seals and O-rings). Partsouq or other sites or Google search can be used to quickly find pictures of relevant components ….

Let’s start at the beginning ….

If previous Posts have been understood correctly, the following AHC components have been replaced with new OEM parts by @suprasvobodea:

-- all four ‘globes’,​

-- all four ‘shock absorbers’,​

-- Height Control Accumulator,​

-- Pressure Sensor (twice),​

-- AHC Pump sub-assembly inclusive of seals and O-rings (not gearcase O-rings),​

-- AHC Fluid.​

There are suspicions about the solenoid valve at the Height Control Accumulator. However, the Height Control Accumulator is NOT vital for bleeding nor for raising the vehicle. The AHC Pump can and will do this, just more slowly, provided that the AHC Pump sub-assembly is able to work correctly.

@suprasvobodea advises that all Height Control Sensors have been opened, inspected and tested electrically per FSM.

The Damping Force Control Actuators, the Control Valve Assembly and the ECU have not been reviewed.

It is unclear how much harness and circuit review has been done and whether or not damaged wiring is a contributor to DTC C1762 on this vehicle.

It is assumed that all AHC-related tests were conducted with wheels on the ground, all doors and rear hatch closed (and no faults in door-light circuit), foot-off-brake (and no faults in brake-light circuit), steering straight ahead, etc, etc (all of which cause AHC conflicts), plus engine started (not just ignition switched “on”).

The vehicle is stuck at LO height (or maybe on the bump stops?), will not raise, and persistently presents Diagnostic Trouble Code (DTC) C1762 with the FSM-specified response time of 0.6 seconds. This DTC C1762 returns almost immediately (0.6 seconds) after it has been cleared by Techstream or manually when the vehicle is re-started.

This means that the AHC/TEMS system is following its settings to protect itself from further damage (and maybe Toyota/Lexus would say protecting the Driver and Passengers from misadventure).

In the case of DTC C1762, as specified in the FSM, the ECU puts the vehicle into “fail safe function” and causes the vehicle to default to the lowest AHC height at any wheel (in this case LO height is reported) and also to default to Step 8 (mid-range of the 16 steps of the damping settings available in TEMS).

No other DTC’s have been reported. (They may exist -- but the quick-acting DTC C1762 may be responding first, masking other fault conditions yet to be revealed).

In this DTC C1762 “fail safe function” condition, the vehicle cannot be raised, nor can there be any continuous auto self-levelling in real time -- which is the basic Active Height Control (AHC) purpose. Nor can there be any continuous real time adjustment across the 16 damping steps, responding to road conditions in real time -- which is the basic purpose of the Toyota Electronic Modulated Suspension (TEMS).

The vehicle will remain in this condition until the cause of DTC C1762 is found and resolved.

The “Active Test” whose full name is the “Height Control Operation Test” cannot be used while DTC C1762 prevails. It is not designed to be used to by-pass the hydraulic protection provided by DTC C1762 or other protective DTC’s. That is not its purpose. To do so would be the hydraulic circuit equivalent of by-passing a burnt-out fuse in an electrical circuit with a nail. We could wish that the designers made different arrangements when the TEMS system was devised and used on the Toyota Soarer in 1983 and later adapted for use in Lexus LX470 in 1998 and onwards and also as an option on some LC100 models. The Toyota/Lexus designers have not changed the design for 100 series – there are differences in the evolution on 200 series and 300 series.

The cause of DTC C1762 on this vehicle remains elusive.

Air in the AHC system seems an extremely likely cause of DTC C1762 on this vehicle given the hydraulic circuit disruptions required for the component change-outs.

Along the way a fault with the AHC Pump has emerged. This is preventing the cause of DTC C1762 from being confirmed and preventing the vehicle from being raised and lowered as part of a normal bleeding process.

Even when connected directly to a 12 volt DC source, weak low pressure Discharge is observed from the overall AHC Pump assembly (the whole thing -- Part Number 48910-60012) on open circuit with Discharge pipe detached. This is described by @suprasvobodea as a dribble from the open Discharge which can be stopped with a finger, even while the AHC Motor and AHC Pump continue to run.

Clearly, AHC Pump does not develop pressure against resistance as it should (and indeed as any positive displacement external gear pump should).

It is the result of a fault in the AHC Pump assembly

There are only the following possibilities for this situation, some are more likely than others. For completeness, here they all are, starting from the motor and working towards the Pump sub-assembly:

• The AHC Electric Motor 88264-60010 is faulty -- this seems extremely unlikely, given that the motor works when connected to 12 volt DC supply,

• The electric motor 88264-60010 is not engaging the Pump sub-assembly 48901-60010 properly – this seems highly unlikely -- but it is worth checking the small connector “shaft” 48977-60010 which passes through the milled aluminium housing 48905-60010 and through a seal 90311-10001. This tiny “shaft” connects the motor on one side of the housing and the driven gear in the Pump sub-assembly 48901-60010 on the other side – and it is worth being satisfied that all parts are engaging properly,

• AHC Fluid is not reaching the Pump sub-assembly 48901-60010 -- this does not seem very likely -- nevertheless it is important to be satisfied that there is no blockage or restriction -- such as might be caused by gel or other gunk -- (a) at the base of the AHC Tank and where it joins on the housing 48905-60010, and (b) that there is no blockage of restriction in the fluid path through the housing 48905-60010 to the point at which the AHC Pump sub-assembly 48901-60010 picks up AHC Fluid. The simplest way to check this might be to remove the Pump sub-assembly and check that there is a good gravity feed of AHC Fluid from the AHC Tank. (I have wondered whether this can be checked by pushing a pipe-cleaner or piece of wire or similar through this passage -- but this might run into the Return Valve within the housing and cause confusion and/or disrupt the Return Valve),

• Air is being drawn into the AHC Pump sub-assembly 48901-60010 -- this is possible and certainly would cause DTC C1762– it is important to be satisfied that the following seals are working as intended, not wrongly fitted, loose, worn or damaged in some way which would allow air ingestion due to negative pressure (sucking) on Intake side of the AHC Pump sub-assembly 48901-60010 when it is operating:
  • seal 90385-08017 between AHC Tank and Housing 48905-60010,
  • Seal 90311-10001 at small connector “shaft” between motor and AHC Pump sub-assembly 48901-60010,
  • Large O-ring 90301-70003 between detachable outer cover 48913-60010 and Housing 48905-60010,

• Any external gear pump (of which the AHC Pump sub-assembly is a micro example compared to industrial scale gear pumps) has a low pressure side (at the Intake) and a high pressure side (at the Discharge).

• In any external gear pump (including the AHC gear pump), the high pressure side and the low pressure side are separated by seals -- the design and location of seals can vary but the principle is always the same,

• In the AHC Pump sub-assembly, the relevant seals are:
  • the triangular-looking O-ring under the top-plate,
  • the O-rings on the gearcases,
  • the small O-ring 90301-06012 where the Discharge from AHC Pump sub-assembly joins the Housing 48905-60010 near the Return Valve,

• If ANY of these three seals weaken or fail, or if during dis-assembly and re-assembly of the AHC Pump sub-assembly the top-plate is insufficiently tightened, then AHC Fluid WILL leak from the AHC Pump sub-assembly into the region behind the outer cover and from there, back to the AHC Tank,

• @BullElk highlighted this situation when he found that the O-rings on the gearcases required replacement and that rectified the no-flow condition in his AHC Pump -- @BullElk had stopped the leak and restored correct AHC Pump operation,

• What it is “The Notch”? Where does it go? In recent Posts by @suprasvobodea, @Moridinbg, @IndroCruise, there have been photographs and stories from three Countries (USA, Bulgaria but travelling in South America, and Australia), where three different knowledgeable people each have opened a package containing a NEW OEM Toyota/Lexus AHC Pump sub-assembly 48901-60010 – this means three separate NEW TOYOTA/LEXUS AHC Pump sub-assemblies fresh out of the box from the factory via IMPEX or PARTSOUQ. There may be other examples from IH8MUD Members but please forgive me if I am unable to recall all of them. Then each of the above persons has taken the top-plate off the sub-assembly -- and lo and behold -- pictures all show the “notch” on the gear-case correctly located (when assembled) below the By-pass Strainer and on Intake side of the AHC Pump sub-assembly!! Probably @BullElk would agree? Similar reports can be found in the 200 series Forum for which the AHC Pump sub-assembly is very similar (although not exactly the same). In the previous Posts this thread, @suprarx7nut also has confirmed the same location and orientation in his own observations. All of that to say that unless someone, somewhere (anywhere!) has better evidence, then that is the end of the story on the correct, as-designed, as-manufactured, purposeful location of the “Notch”.

• What is the purpose of the “Notch”? The “Notch” is an obvious and deliberate effort by the Pump designer/manufacturer to facilitate an exit pathway for the fluid trapped in between the meshing gear teeth as they emerge from the mesh. A different approach might have been to manufacture larger clearances between the components -- but that have may detracted from Pump performance. So the “Notch” is a compromise probably made to simplify manufacturing of a mass-produced item,

• The high pressure fluid trapped in the gear mesh requires an exit path. This fluid cannot fight with the incoming fluid because then there would be no pressure difference to create a Discharge, just fluid going round and round inside the Pump. In gear pumps this exit path is via the fine clearances around the gearcases. In the AHC Pump, this path leads to the area in the top-plate surrounded by the triangular O-ring. Further exit is blocked by the O-rings on the gearcases in the AHC Pump sub-assembly -- provided that these O-rings are in good condition,

• The exiting fluid then moves from the area within the triangular O-ring and passes through the By-pass filter and then on to the Intake side of the AHC Pump sub-assembly,

• In the AHC gear pump, the fluid in this exit path is at very high pressure -- this has the intended added benefit of increasing the pressure on the gearcases which in turn increase the force pressing the gears onto the floor of the housing, reducing clearances and reducing the fluid bypassing across the top and bottom surfaces of the gears, and enhancing Pump performance at the Discharge,

• There is a balance here -- if the top-plate is insufficiently tightened, then that can easily be the cause of multiple kinds of leakage within and from the AHC Pump sub-assembly to the outer case and the AHC Tank and be the cause of low flow and low pressure at the AHC Pump sub-assembly Discharge. If the top-plate is over-tightened, then that may inhibit gear rotation and cause the tiny connector “shaft” between the Motor and the AHC Pump sub-assembly to disengage or be damaged, resulting in reduced flow and pressure at the discharge (or maybe no flow at all),

• I mean no criticism or offence whatsoever to @suprasvobodea or anyone else when I say that in my personal opinion from far way, the cause of lack of discharge from the AHC Pump in the subject vehicle is due to the dis-assembly and re-assembly of the AHC Pump sub-assembly with the top-plate insufficiently tightened – resulting in loss of Discharge pressure and flow due to internal FLUID leaks at the seals. There is nothing about dis-assembly and re-assembly of the AHC Pump sub-assembly in the FSM -- so it is a matter of trial and error by those who choose to do so. The alternative is to replace Pump sub-assembly 48901-60010 as recommended by Toyota/Lexus,

• @suprasvobodea has advised that when he re-installed his new AHC Pump sub-assembly 48901-60010, with the “Notch” on the wrong side, there was no Discharge, and the Motor had stalled in an over-current situation (hot leads). This is a new Pump, clearances are tight, it cannot work this way, so personally I don’t find ‘hydraulic lock-up’ surprising, because the fluid exiting the meshing gear teeth has nowhere to go,

• @Moridinbg has described some different experiences while nursing an old AHC Pump sub-assembly in his LC100 while traversing most of South America, including experiments with the “Notch” positioned on either side of the Pump and also reversing the polarity of the Pump Motor. Having followed his “Re-build” thread and his “Patagonia” thread, I can only salute the resourcefulness and ingenuity of @Moridinbg, both in the workshop in Bulgaria, and while doing diagnosis and roadside repairs in extremely remote environments in South America. I do wonder whether some of the effects he observed may be due to wear-related increase in clearances within the Pump, or, gearcase O-rings possibly were past their best? Only @Moridinbg could answer that ….

The attached Paper "The Fundamentals of Gear Pump Design" -- US Naval Research Laboratory - January 2022 -- may be of interest to those with an interest in the technicalities ....

This video may be a bit too long -- it shows a Master Mechanic instructing a young Apprentice on the workings of a gear pump and the location and purpose of the internal seals and the by-pass arrangements along the gearcase clearances. The example is a large-scale gear pump used to drive a log-splitting machine. The details are different but the principles are the same as in the tiny AHC Pump sub-assembly.

 

[suprarx7nut]

Sooo.... @suprasvobodea How goes it?!

 

[suprasvobodea]

Sooo.... @suprasvobodea How goes it?!

Sooo.... @suprasvobodea How goes it?!

SupraRX7


I was just about to reply to you and INDOCRUISW with the update later today, but since you were so kind to check in with me, I will do it now. You and INDOCRUISE are correct about this simple gear pump. It is a VERY simple concept and should work if there is fluid in it- I'm a Mechanical Engineer,, so i get that! .
The description below is with the replacement pump that has never been used, but I DID OPEN IT UP ( STUPID !) I have another new pump (AHC Pump sub-assembly 48901-60010) on order from IMPEX and i hope it will arrive by Friday. Until then, I want to see if this new pump that i have can work again.

I did as you described, and just filled the pump assy with oil, BEFORE attaching the reservoir so I could "burp" the pump housing by holding it at an angle where you can see that opening in the top of the AL pump housing that the tank grommet fits into. ( BTW- I bought a NEW grommet for that interface between the reservoir and AL pump housing. ) I watched the bubbles rise as I filled the pump through the 1" wide opening. When the fluid was no longer going into the pump gear area and was filled to the top of that opening, I applied 12 V directly to the pump and no fluid stream emerged when I removed the rubber stopper from the outlet ( I ll attache pictures when I go back to the garage to take them in about an hour) THIS..... IS A PROBLEM .. all i can figure out is it means ... there is still air INSIDE the gear pump housing as it is NOT sealing inside it. There is no pressure resistance to since the outlet is open to the atmosphere, but it should still send out a stream of oil like it did before I removed it from the LX and disassembled it to check the inlet and outlet tiny screens!!! NOW,..... I wish i would have NEVER done that .....

Well , I topped off the opening where the reservoir attaches and applied 12 V to the motor and got NOTHING! No fluid movement from the little pool in that opening . S I wish we could attach a video, but the forum says I have to have a . PNG or. GIF file, not a . MOV file so I cannot! I do appreciate all Ya'll help with this, YOU, INDOCRUSIE, 2001LC, MORIDINLG, and everyone who has contributed to this post. This is a wonderful gift and tool to help all of us, on a personal level. THANK YOU!